The art is generally aware of insect bait stations for crawling insects that have a base with various topographical features and with a cover that spans those features to create an enclosed bait station. Examples include Woodruff et al., U.S. Pat. No. 4,536,836; Brandli, U.S. Pat. No. 4,894,947; Brandli, U.S. Pat. No. 5,048,225; Morris, U.S. Pat. No. 4,485,582; Mares, U.S. Pat. No. Des. 306,895; Mares, U.S. Pat. No. Des. 326,890; Wissman, U.S. Pat. No. 4,782,612; Gentile, U.S. Pat. No. 4,793,093; Demarest et al., U.S. Pat. No. 4,823,506; Demarest, U.S. Pat. No. 4,837,969; and Lin, U.S. Pat. No. 5,357,709. This list is by no means intended to be comprehensive, this being a crowded art.
Commonly, though not universally, these bait stations employ features such as walls or passageways that are unitarily formed as parts of the base of the bait station. The cover associated with such a base typically spans these structures without significantly obstructing them.
Woodruff et al., U.S. Pat. No. 4,563,836, is an example of this sort of structure, the base portion of the Woodruff et al. insect feeding station including outer and inner walls with openings in them through which insects can pass. In Woodruff, all of these features are formed as a unitary piece of a flat, deformable sheet of plastic or other material. The Woodruff et al. cover spans all of these features. All portions of the cover remain elevated well above the floors of the openings that are formed in the walls, leaving these openings sufficiently unobstructed that an insect can pass through them. Except for its relatively shallow rim, the Woodruff et al. cover itself is a generally flat, featureless structure, an arrangement not uncommon among the bait stations noted above.
The bait station of Demarest, U.S. Pat. No. 4,837,969, utilizes a different approach. In Demarest, '969, the base includes a number of upwardly projecting features. The cover, however, instead of simply being flat, includes as parts of the cover the exterior side walls of the bait station. The cover of Demarest '969 thus constitutes a shell that fits down over and interacts with the underlying structures of the base. The doors by which insects can enter the Demarest '969 bait station are formed not as gaps in or between walls rising from the base but instead are holes in the shell portion of the cover.
The cover of a bait station such as that of Demarest '969 must be capable of bearing a certain amount of top loading without being crushed. Thin walls for the shell are desirable in order to reduce the amount of plastic used in manufacture, thus contributing to the economy of the bait station. But thinning the walls reduces their strength and crush resistance.
In Demarest '969, inner walls, shown at 14 in FIG. 2 of Demarest '969, are formed as a part of the base and provide support for the cover. The geometry of the Demarest '969 bait station is such that these walls may be longitudinally extended, projecting radially from a central well 18 (seen in FIG. 2 of Demarest '969) toward the outermost portions of the cover. This arrangement is accommodated by the "multi-lobed" design of the cover, as disclosed in Demarest '969. Thus the cover of Demarest '969 may be thin and relatively flexible in that it need span only the modest width of the bait well of the bait station. However, the arrangement does subdivide each lobe of the cover, thus blocking the movement of insects around the periphery of the interior of the bait station.
An ongoing need still exists in the art for a bait station for crawling insects that utilizes a cover that has a shell that may be made of thin materials but that is used in association with a base having structures that provide longitudinally extended support for the shell such that the shell can span relatively great distances with adequate crush resistance, such bait station still providing ready access to bait held within the bait station for insects entering doors formed in the shell.